The present invention relates in general to the manufacture and assembly of small sized, three dimensional antennas, such as, but not limited to, precision wound helical antennas of the type used for very high frequency phased array antenna applications (e.g., several GHZ to several tens of GHz). The invention is particularly directed to a low cost, reduced complexity antenna fabrication scheme, that forms a three-dimensional antenna of a contoured section of flex circuit. The signal coupling interface for the antenna is effected by means of a section of transmission line feed electromagnetically coupled to the flex circuit.
As described in the above-referenced ""073 application, recent improvements in circuit manufacturing technologies for small sized components used in high frequency communication systems have been accompanied by the need to reduce the dimensions of both signal processing components and interface circuitry support hardware, as well as their associated radio frequency antenna structures. Such reduced size, high frequency communication systems, including those containing phased array antenna subsystems, often employ a distribution of three-dimensionally shaped antenna elements, such as helical antenna elements wound on low loss foam cores. These types of antenna elements are particularly attractive for such systems, as their radiation characteristics and relatively narrow physical configurations readily lend themselves to implementing physically compact, phased array architectures, that provide for electronically controlled shaping and pointing of the antenna""s directivity pattern.
However, as operational frequencies of communication systems have reached into the multi-digit GHz range, achieving dimensional tolerances in large numbers of like components, particularly at low cost, has become a major challenge to system designers and manufacturers. For example, each antenna element of a relatively large numbered element phased array antenna operating at frequency in a range of 15-35 GHz, and including several hundred to a thousand or more antenna elements, for example, may contain on the order of twenty turns, helically wound within a length of only several inches and a diameter of less than a quarter of an inch.
Although conventional fabrication techniques, such as that diagrammatically shown in the perspective view of FIG. 1, which uses a pair of crossed-slot templates 11 and 12 to form a helically configured antenna winding 14, may be sufficient for relatively large sized applications (since relatively small variations in dimensions or shape may not significantly degrade the electrical characteristics of the overall antenna), they are inadequate for replicating large numbers of very small sized elements (multi-GHz applications), where minute parametric variations are reflected as a substantial percentage of the dimensions of each element. In such applications, it is imperative that each antenna element be effectively identically configured to conform with a given specification; otherwise, there is no assurance that the overall antenna architecture will perform as intended. Namely, lack of predictability is effectively fatal to the successful manufacture and deployment of a high numbered multi-element antenna structure, especially one that may have up to a thousand elements, or more.
Advantageously, the invention described in the ""073 application successfully overcomes such drawbacks of conventional helical antenna assembly techniques for high frequency designs, through a precision, cast core-based manufacturing process that is capable of producing large numbers of very small helically wound antenna elements, each of which has the same predictably repeatable configuration parameters. A helically wound antenna produced by the cast core-based fabrication scheme of the ""073 application is diagrammatically illustrated in the side view of FIG. 2, as comprising an integrated arrangement of a cup-shaped, core-support structure 20, into which a precision molded dielectric core 30 is retained, with a multi-turn wire 40 being wound in a helical groove 42 formed in the outer surface of the dielectric core 30. The cup-shaped core-retaining support structure 20 is also configured to house a baseplate, a tuning circuit for the antenna, as well as a standard, self-mating connector 50 for interconnecting the antenna to an associated transmit-receive module.
The precision molded dielectric core 30 comprises a generally cylindrically shaped, elongated dielectric rod, having a base end 31 affixed to the cup""s baseplate 20. A major length portion 32 of the dielectric rod has a constant diameter cylindrical shape adjoining a tapering portion 33, that terminates at a distal end 34 of the core. The helical groove 42 is precision-formed in the outer surface of the core 30, and serves as a support path or track for a length of antenna wire 40 tightly wound in the core""s helical groove 42, leaving wire extensions that project from the base end 31 and the distal end 34 of the core 30.
The wire 40 is adhesively secured in the core groove to realize a dielectric core-supported helical winding that is dimensionally stable, and conforms exactly with the precision helical groove 42. The antenna wire-wrapped core is mechanically and electrically attached to the cup-shaped core support structure 20, so that the antenna may be physically mounted to a support member and connected to an associated transmit-receive module. Within this support structure 20, the feed end of the helical antenna wire 40 is physically attached to the center pin of the self-mating connector 50 by means of soldering, for example, so that the connector 50 may provide a direct low loss connection to the transmit-receive module, as described above.
Now, even through the antenna architecture and associated fabrication scheme described and shown in the ""073 application provides a significant improvement over conventional small dimensioned antenna production schemes, in terms of repeatability for applications requiring large numbers of very small sized antenna elements, it still requires the use of a direct, hard wired (e.g., solder) connection between the antenna""s radiating/sensing wire and feed connector, which implies substantial packaging and cost of assembly.
In accordance with the present invention, these drawbacks are substantially obviated by a low cost, reduced complexity antenna fabrication scheme, that employs a section of a thin, lightweight flex circuit decal, rather than a wire, as the antenna""s radiating element. In order to support and contour the flex circuit decal in its intended three-dimensional shape, the flex circuit is attached to a support core that conforms with the intended (three-dimensional) shape of the antenna. In order to reduce the hardware and assembly complexity of using an electro-mechanical connector to interface the radiating/sensing wire and its associated feed, the signal coupling interface for the antenna is formed by electromagnetically coupling of a section of transmission line to the flex circuit.
For the non-limiting example of forming a helically configured antenna, the core may be generally cylindrically configured so as to conform with the intended geometric shape of the antenna winding. A relatively thin, dielectric-coated ribbon-configured conductor, such as a generally longitudinal strip of polyimide-coated copper conductor or xe2x80x98flex-circuitxe2x80x99, is wound around and adhesively affixed to the outer surface of the core thereby forming a xe2x80x98decalxe2x80x99-type of helical antenna winding. This enables the flex circuit to be effectively surface-conformal with the core and thereby conform precisely with the intended geometric dimensional parameters of the antenna. To facilitate accurately conforming the flex circuit with a prescribed shape that produces the intended radiation profile of the antenna, placement aides, such as fiducial alignment marks may be provided, or a channel may be patterned in the outer surface of the core by means of a robotic machining, placement and assembly apparatus.
In addition to being wound around and affixed to the core""s cylindrical surface the flex circuit extends to a generally planar underside region of a base portion of the core. By wrapping around and attaching this additional length of flex circuit to the underside of the base portion of the core, the winding extends to a location for proximity electromagnetic coupling with a similarly configured section of microstrip feed provided on a dielectric substrate such as the front facesheet of a panel-configured antenna module. The feed-coupling section of the flex circuit is separated from the flex circuit-coupling feed section of the microstrip feed by a thin insulator layer, such as the polyimide coating layer of the feed-coupling section of the flex circuit. This dielectrically isolates the flex circuit from the microstrip feed, yet provides for electromagnetic coupling therebetween. Relatively narrow dimensions of the mutually overlapping and electromagnetically coupled flex circuit and microstrip feed sections provide a connectorless integration of the three-dimensional antenna affixed to the core with signal processing elements that are electrically interfaced with one or more locations of the microstrip separated from the antenna.